Process for recovering precious metals from clay-containing ores

ABSTRACT

A solution for leaching metals from clay containing ore and a method of leaching ore is described. The solution comprises a cyanide; a wetting agent; and a clay stabilizing polymer.

BACKGROUND

The present invention is related to an improved process for recoveringmetals, particularly precious metals, from clay-containing ores. Morespecifically, the present invention is related to the use of specificpolymers and wetting agents for improved metal recovery from clay.

Heap leaching is an industrial mining process for the extraction ofmetals such as gold, silver, copper, uranium, and other compounds fromore. The process includes the use of chemical reactions to formcomplexes with specific minerals and then releases these minerals aftertheir division from other earth materials. Similar to in situ mining,heap leach mining differs in that it places ore on a liner withchemicals added via drip systems to the ore.

The mined ore is usually crushed into small chunks and heaped on animpermeable plastic and/or clay lined leach pad where it can beirrigated with a leach solution to dissolve the valuable metals. Whilesprinklers are occasionally used for irrigation, drip irrigation ispreferred to minimize evaporation, provide more uniform distribution ofthe leach solution, and to avoid damaging the exposed mineral. Thesolution percolates through the heap and leaches both the target as wellas other minerals. This process, called the “leach cycle,” generallytakes one or two months for simple oxide ores, such as most gold ores,to two years for other ores such as nickel laterite ores. The leachsolution containing the dissolved minerals is typically collected,treated in a process plant to recover the target mineral and in somecases precipitate other minerals, and then recycled to the heap afterreagent levels are adjusted. Ultimate recovery of the target mineral canrange from 30% of contained ores, such as run-of-mine dump leachingsulfide copper ores, to over 90% for the easiest to leach ores such assome of the oxide gold ores.

The crushed ore is irrigated with a dilute alkaline cyanide solution.The solution containing the dissolved metals, typically referred in theart as pregnant solution, continues percolating through the crushed oreuntil it reaches the liner at the bottom of the heap where it drainsinto a storage pond which is often referred to in the art as a pregnantsolution pond. After separating the metals from the pregnant solution,the dilute cyanide solution, typically referred to in the art as a“barren solution”, is normally re-used in the heap-leach-process oroccasionally sent to an industrial water treatment facility where theresidual cyanide is treated and residual metals are removed. In veryhigh rainfall areas, such as the tropics, in some cases there is surpluswater which may be discharged to the environment, after treatment. Thispractice can cause water pollution if improperly performed.

The process generates a large volume of waste material and is ratherburdensome on a large scale. By way of example, the production of theequivalent of one gold ring through the heap method can generate 20 tonsof waste material.

During the extraction phase, gold ions are solubilized by formingcomplex ions with cyanide:Au¹⁺(s)+2CN⁻(aq)→Au(CN)₂ ⁻(aq)According to J. B. Hiskey, Arizona Bureau of Geology and MineralTechnology Fieldnotes, Vol. 15, No. 4, Winter 1985, gold is dissolved inan aerated cyanide solution according to the following two-step reactionsequence:2Au+4CN⁻+O₂+2H₂O→2Au(CN)₂ ⁻+2OH⁻+H₂O₂  (1)2Au+4CN⁻+H₂O₂→2Au(CN)₂ ⁻+2OH⁻  (2).

Recuperation of the gold is readily achieved with a redox-reaction orwith electrowinning, also called electroextraction, wherein metals areelectrodeposited from their ores that have been put in solution.Electrorefining uses a similar process to remove impurities from ametal. Both processes use electroplating on a large scale and areimportant techniques for the economical and straightforward purificationof non-ferrous metals.

In electrowinning, a current is passed from an inert anode through aliquid leach solution containing the metal. The metal is extracted as itis deposited in an electroplating process onto the cathode. Inelectrorefining, the anodes consist of unrefined impure metal. As thecurrent passes through the acidic electrolyte the anodes are corrodedinto the solution so that the electroplating process deposits refinedpure metal onto the cathodes.

Clay in ore can interfere with the leaching process. Certain clays canhydrate and swell when exposed to the aqueous leaching solution. Theswollen clay particles can slow or block the flow of leaching solutionthrough the heap and thus reduce leaching productivity. Therefore, thereis a need in the mining industry for materials or processes whichminimize the deleterious effects of clay swelling on heap leachingproductivity.

In spite of the ongoing effort those of skill in the art still do nothave a suitable option for mitigating the productivity losses associatedwith clay in heap leaching.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved solution forextraction of metals, particularly precious metals, from clay and animproved process related thereto.

It is another object of the invention to provide a solution whichincreases the efficiency of metal extraction, particularly preciousmetals extraction, from clay without alteration of the extraction bed orprocess steps.

These and other advantages, as will be realized, are provided in asolution for leaching metals, particularly precious metals, from claycontaining ore comprising: cyanide; a wetting agent; and a claystabilizing polymer.

A method for heap leaching of metals from clay containing orecomprising: forming a heap of ore on a leach bed; percolating a leachsolution through the heap wherein the leach solution comprises cyanide;a wetting agent; and a clay stabilizing polymer; thereby forming apregnant leach solution comprising the precious metal; and removing theprecious metal from the pregnant leach solution.

FIGURES

FIG. 1 is a graphical representation of an embodiment of the invention.

FIG. 2 is a graphical representation of an embodiment of the invention.

FIG. 3 is a graphical representation of an embodiment of the invention.

DESCRIPTION

The instant invention is directed to the addition of certain additivesto the cyanide based heap leaching solution to increase percolationrates of the solution through the heap, or at least to minimize drop offin leaching rates with time. More specifically, the present invention isdirected to a leach solution for improved extraction of metals from claywherein the solution comprises cyanide, a wetting agent and at least oneclay stabilizing polymer additive.

Crude clay deposits, such as Georgia kaolins, contain micrometer-sizeparticles, ranging in size from about 0.1 microns to 15 microns.Particles at the smaller end of this range tend to be plate-like inshape, with their diameters about 6 to 10 times their thickness. Largerparticles comprise stacks of particles that adhere in a face-to-facemanner, like a stack of coins. Larger, granular clay particles can bebroken down into smaller, delaminated particles by splitting the layeredstacks into thin, plate-like units. Clay is a naturally occurringmineral in the phyllosilicate category, consisting of aluminum silicateas a principal component, along with various other metals such ascalcium, potassium and magnesium, with varying levels of water content.Clays are formed from alternating sheets of tetrahedral SiO₄ andoctahedral AlO₄, with the two sheets forming a layer. If a layerincludes only one silica sheet and one alumina sheet, it is termed a 1:1clay. Kaolin is an example of such a clay. These layers are tightlyattached through hydrogen bonding. If, on the other hand, a layer ismade of three sheets, as a silica-aluminum-silica sandwich, the clay istermed a 2:1 clay. Layers are attached to each other by van der Waalsforces. There is a gap of about 1 nm between the layers, called the“gallery,” where various cations such as sodium, magnesium, calcium andlithium may reside. The smectite family of clays, such asmontmorillonite, hectorite and saponite are 2:1 clays.

While not limited to theory, it is hypothesized that the clays shear, orbecome separated along faces, in the presence of water thereby exposinghydrophilic portions which migrate, or wick, with the water flow. Theresult is believed to be a physical plugging of flow paths of thecyanide solution thereby reducing the effectiveness of the leachingoperation. Still without limit to theory, it is hypothesized that theclay stabilizing polymer additive stabilizes the clay by impeding thebreakdown of the clay particles thereby minimizing their ability toblock flow passages. Further without limit to theory, the wetting agentis believed to improve the function of the clay stabilizing polymeradditive with regards to the ability of the polymer additive tostabilize the clay.

The leach solution is preferably basic. More preferably, the leachsolution has a pH of at least 8 to no more than about 11. Below a pH ofabout 8 the reaction of the cyanide with the metal is inefficient. Abovea pH of about 11 the leach solution is caustic which increases handlingdifficulties and increases the rate of equipment corrosion. A pH ofabout 9.5 to 10.5 is optimal.

The clay stabilizing polymer additive is selected from a polyalkyleneoxide copolymer; propoxylated glycols; polyamine copolymers comprisingdicyandiamide, formaldehyde and ammonia; polyvinyl alcohol; partiallyhydrolyzed polyvinyl acetate; polyacrylamide; quaternary amines andparticularly tetramethyl ammonium salts; carboxymethyl cellulose;methacrylate copolymers; hydroxyaldehydes; hydroxyketones; andcopolymers of anionic or cationic monomers, more preferably cationicmonomers. Particularly preferred is a clay stabilizing polymer additiveselected from a polyalkylene oxide copolymer, propoxylated glycols andpolyamine copolymer comprising dicyandiamide, formaldehyde and ammonia.The clay stabilizing polymer absorbs onto the clay or shale therebyinhibiting separation through shearing. The clay stabilizing polymeradditive is either a high molecular weight polymer with limitedsolubility, which is believed to cause the polymer to form somewhat of abarrier on the clay, or a charged species which electrostatically formsa barrier on the clay.

The polyalkylene oxide copolymer preferably comprising a polypropyleneoxide (PO) block, and at least one polymeric block selected from thegroup consisting of polyethylene oxide (EO), aromatic polyester, andaliphatic polyester.

More specifically, the polyalkylene oxide copolymer is defined byformula:R¹—R²—R³R⁴—R⁵wherein:R¹ and R⁵ are terminal groups independently selected from the groupconsisting of H, hydroxyl, saturated or unsaturated aliphatic of 1 to 30carbons, —OC(O)R⁶ wherein R⁶ is a hydrogen or a saturated or unsaturatedaliphatic of 1 to 30 carbons;at least one of R², R³ or R⁴ is polypropylene oxide (PO) with 1 to 100PO groups and preferably 2 to 100 PO groups;R², R³ or R⁴ is otherwise independently selected from the groupsconsisting of: polyethylene oxide (EO) with 1 to 100 EO groups andpreferably 2 to 100 EO groups; polypropylene oxide (PO) with 1 to 100 POgroups and preferably 2 to 100 PO groups with the proviso that at leastone of R², R³ and R⁴ is not PO; polyester defined by—(OC(O)R⁷C(O)O)_(z)— wherein R⁷ is aromatic with at least one to no morethan four aromatic rings or a saturated or unsaturated aliphatic with 1to 20 carbons and z is an integer of 1 to 100 and preferably 2 to 100.In a preferred embodiment R³ is PO and R², R³ and R⁴ are independentlyselected from EO and polyester.

The polyalkylene oxide copolymer preferably comprises PO and EO with theratio of PO/EO being at a ratio sufficient to maintain a low solubilityin water and have high affinity for the clay particle surface. It ispreferable that the polyalkylene oxide copolymer have low solubility inwater. However, it is preferable that the polyalkylene oxide copolymerhave enough water solubility to be dispersible in water thereby allowingthe polyalkylene oxide copolymer to be delivered from water and toadsorb over the surface of the clay particles so some level ofsolubilizing groups is believed to be necessary. A high level of PO inthe polymer increases its affinity for the clay surface and decreasesits water solubility so that it is not easily washed off in the leachingprocess. It is particularly preferred that the polyalkylene oxidecopolymer have at least 10% up to 50% EO and at least 40 to 90% PO withthe proviso that the low solubility is realized. The polyalkylene oxidecopolymer needs to have a molecular weight and polymer chain lengthsufficient to enable the polymer to cover the clay particle sufficientlyto slow the exfoliation process. Longer blocks of polypropylene glycolin the copolymers increase the affinity for coating clay particlesreduce its proclivity to wash off during the leaching process.

Alkoxylated glycols comprise a glycol backbone with repeat units derivedfrom alkylene oxide. More specifically, the alkoxylated glycols aredefined by the formula:X[(CH₂CHR¹⁷O)_(s)R¹⁸]_(t)wherein X is a linking group derived from an organic compound containingat least two hydroxyl or amine groups capable of reacting with ethyleneoxide;each R¹⁷ is independently —H or —CH₃, branched or linear aryl or alkylmoieties of 2-22 carbons which can be unsubstituted or substituted, andmay also be —CH₂OR¹⁹ groups such as those arising from the reaction ofan alkyl or aryl glycidyl ether with the proviso that at least one R¹⁷is not hydrogen;each R¹⁸ is independently —H, unsubstituted or substituted aryl or alkylhydrocarbon chains of 1-25 carbons which may be saturated orunsaturated, or an ester group —C(═O)R²⁰;R¹⁹ is a branched or linear aryl or alkyl moiety of 1-22 carbons whichcan be substituted or unsubstituted;R²⁰ is unsubstituted or substituted aryl or alkyl hydrocarbon chain of1-25 carbons which may be saturated or unsaturated;s is an integer of 3-300;t is an integer of 2-12.

The linking group, designated X in Formula 1, is selected from polyolsand polyamines comprising at least two reactive alcohol or aminehydrogens. The linking group may comprise a linear or branched,optionally substituted, alkyl of 3-100 carbons. In one embodiment, allof the labile alcohol or amine hydrogens are derivatized to form apendant group attached thereto, however in other embodiments alcoholsand/or amines remain to increase the hydrophilicity of the core.Particularly preferred linking groups are selected from the groupconsisting of ethylene glycol, ethylene diamine, ethylene triamine,glycerin, trimethylol propane, pentaerythritol, sorbitol, sorbitan,diglycerol, triglycerol, higher polyglycerols, and polysaccharides orother polyols such as polyvinyl alcohol with a molecular weight of up to400 Da.

A particularly preferred alkoxylated glycol is defined by the formula:R¹⁰—CH₂—CH(OR¹²)CH₂(OCH₂CH(OR¹³)CH₂)_(n)OR¹¹wherein R¹⁰ and R¹¹ are terminal groups independently selected from thegroup consisting of H, hydroxyl, saturated or unsaturated aliphatic of 1to 30 carbons; or OC(O)R¹⁵ wherein R¹⁵ is a hydrogen or a saturated orunsaturated aliphatic of 1 to 30 carbons;R¹², R¹³ are independently selected from polyethylene oxide (EO) with 1to 100 EO groups and preferably 2 to 100 EO groups; polypropylene oxide(PO) with 1 to 100 PO groups and preferably 2 to 100 PO groups; or—(CH₂CHR¹⁶O)_(r)— wherein each R¹⁶ is independently hydrogen or methyland r is an integer of 1 to 100 and preferably 2 to 100 and n is aninteger of 1 to 4.

The polyamine copolymer is defined as comprising dicyandiamide,formaldehyde and ammonia with a hydroxyl number of at least 20 to nomore than 35 and more preferably a hydroxyl number of at least 26 to nomore than 31. Below a hydroxyl number of 20 the polyamine isinsufficiently bound to the clay and therefore the benefits are muted.Above a hydroxyl number of 35 the solubility increases thereby mutingthe ability of the polyamine copolymer to precipitate onto the surface.

The cyanide solution is an aqueous solution preferably comprises atleast 50 ppm cyanide to no more than 1000 ppm cyanide. Below about 50ppm cyanide the rate of extraction of the metals is insufficient forcommercial use. Above about 1000 ppm the rate of extraction of themetals is not increased to the degree necessary to justify theadditional material usage. More preferably, the cyanide solutioncomprises at least about 200 to no more than about 800 ppm cyanide

The wetting agent is preferably selected from the group consisting ofalcohol alkylates preferably chosen from alcohol ethoxylates and alcoholpropoxylates; polyethylene glycol esters with 3 to 20 and morepreferably 7 to 12 polyethylene groups; hydrophilic modified silicones,fatty amine ethoxylates and sulfosuccinates, particularly dioctyl sodiumsulfosuccinate (doss).

Alcohol ethoxylates are non-ionic surfactants composed of an alkyl chainwith 5-20 carbon atoms, and more preferably 10-15 carbon atoms, combinedwith 2 to 20 ethylene oxide units, and preferable 3 to 14 ethylene oxideunits.

In the process for extracting metals from clay rich ore the mined ore iscrushed into small particles to increase the surface area. The crushedore is then placed on a leach pad with an impermeable plastic and/orclay lined leach pad in thick regions referred to as heaps. The heapsare then treated with leach solution comprising cyanide, wetting agent,and a polymer as described elsewhere herein by any technique known inthe art such as drip irrigation, sprinkling and the like such that thesolution percolates through the ore leaching out precious metals as itpercolates thereby forming a pregnant leach solution. The pregnant leachsolution is then treated to isolate the metals. In a preferredembodiment the leach solution, after isolation of the metals therefrom,is regenerated by adding depleted chemicals and then reused as recycledsolution.

Throughout the description terms such as aliphatic, aromatic and alkylrefer to either substituted or unsubstituted groups. The terms aliphaticand alkyl refer to saturated and unsaturated unless otherwise specified.

EXAMPLE 1

Two techniques were used to measure the effectiveness of the inventivesolution. One technique was a flow through method utilizing a columnassembly wherein the solution was allowed to flow through the columnwith aspirator vacuum assist. A second technique utilized a slurrywherein the solution being tested was mixed with soil and laterseparated from the soil by filtration.

For the flow through method, a column assembly was prepared using aBuchner funnel fitted with a #4 Whatman filter. A polyethylene column ofdifferent heights was formed from a cylindrical sleeve cut frompolyethylene sample bottles. The column assembly was placed on a filterflask connected to a sink aspirator. The column was charged with 100 mlof soil followed by flow through extraction with 100 mL of solutionunder aspirator vacuum to facilitate liquid leaching through the soil.

For the slurry method 100 mL of soil was introduced into a 500 mL beakerfollowed by addition of 100 mL of solution. The materials were swirledfor approximately 5 minutes to completely wet the soil. The slurry wasallowed to sit for 60 minutes followed by filtration of the slurry usinga Buchner funnel fitted with a #4 Whatman filter with aspirator vacuumassist.

In the Tables samples A1-A5 were tested by the column method and samplesB1-B5 were tested by the slurry method. A stock extract solution of 500ppm NaCN was formed by diluting 125 mL of 2.5% NaCN with 500 mL water toform 625 mL of solution. A spiked extract solution was made by adding 2g of additive to 198 g of the 500 ppm NaCN stock extract solution. Ineach case the amount of liquid recovered was determined as was themetals extracted. Results are presented in Table 1 wherein “Solution”lists the additive. The column labelled “Drop” reports the time requiredto collect the first drop of liquid. The column labelled “100 mL”reports the time required for loading 100 mL of extracting solution intothe funnel.

TABLE 1 Solution 100 mL Collected Sample Additive Soil (g) Drop(min:sec) (min:sec) (g) Comment A1 — 134.13 8:20 29:30 55.68 A2 CS-1550134.28 7:40 31:00 56.1870 A A3 CS-1420 134.27 0:50  7:25 63.5577 A4CS-1420ST 134.22 3:39 14:25 59.1784 A5 Ethox 4439 134.28 0:41  7:0063.5230 B B1 — 134.30 59.4055 B2 CS-1550 134.25 59.2633 C B3 CS-1420135.55 57.1100 B4 CS-1420ST 134.43 60.2596 D B5 Ethox 4439 134.1153.8605

In the comments of Table 1, A indicates the solution was light orangeand turned darker after sitting, B indicates the material foamed duringfiltration, C indicates the solution was dark orange and D indicatesthat the vacuum pulled gas from solution.

For the purposes of the experiments, NaCN was purchased as 2.5% (w/v)from LabChem, Inc. Zelienople, Pa. Cat #LC23700-7 lot #D008-12 Exp Jan.9, 2016. HPLC grade water was used unless otherwise stated. CS-1550, avery low molecular weight, high charge density polyamine claystabilizer, was obtained from Polymer Ventures of Charleston, S.C. It isbelieved to be a terpolymer of dicyandiamide, formaldehyde, and ammoniumchloride. CS-1420 is a low molecular weight, high charge densitypolyamine clay stabilizer obtained from Polymer Ventures of Charleston,S.C. CS-1420ST is a salt tolerant low molecular weight, high chargedensity polyamine clay stabilizer available from Polymer Ventures ofCharleston, S.C. Ethox 4439 is a commercially available ethyleneoxide-propylene oxide-ethylene oxide block copolymer with 40% ethyleneoxide available from Ethox Chemicals, LLC as P-104. Extracts ofcollected solution were sent to Nevada Analytical Services in Reno, Nev.89502 for analysis by ICP-AES. The results are presented in Tables 2-4wherein the metal is reported in ppm relative to the extract in Table 2,in mg in the extract in Table 3, and in ppm in soil in Table 4.Reporting as concentration in soil normalizes the results in terms ofthe amount of extract collected as well as the amount of soil tested.

In Tables 2-4 soil and solution collected are reported in grams, NDindicates below reporting limit, i.e., <0.25 ppm for Au and Ag, <0.20ppm for Hg, NA indicates not applicable. The amount of each metal in theextract was calculated by the formula: A=(B×C)/1000 wherein: A is theamount of metal in extract in mg, B is the amount of extract in gramsand C is the concentration in the extract in ppm. Concentration ofmetals in the original sample were calculated by the formula:D=1000×A/E, wherein A is the amount of metal in extract in mg; D is theconcentration of metals in the original sample in ppm, E is the amountof soil tested in grams. The results are provided in Table 2. In theresults provided in Table 2 gold was not detected. Extraction of Au wasnot observed due to the low level of Au in the soil and the test scale.Based on expected correlation Ag and Hg extraction efficiencies areexpected to correlate to Au extraction. In Table 2 the metals aredetermined from ore extract and reported in ppm relative to the amountof extract. In Table 3 the metals are determined from ore extract andare reported in mg in the extract. In Table 4, the metals are determinedfrom ore extract, reported in ppm relative to the amount of soil.

TABLE 2 Solution Collected Au Ag Hg Sample Soil (g) (g) (ppm) (ppm)(ppm) A1 134.13 55.6800 ND 0.27 0.34 A2 134.28 56.1870 ND 0.50 0.60 A3134.27 63.5577 ND ND 0.25 A4 134.22 59.1784 ND 0.29 0.44 A5 134.2863.5230 ND ND 0.20 B1 134.30 59.4055 ND ND 0.28 B2 134.25 59.2633 ND0.26 ND B3 135.55 57.1100 ND 0.29 0.40 B4 134.43 60.2596 ND ND 0.27 B5134.11 53.8605 ND ND 0.27

TABLE 3 Solution Collected Au Ag Hg Sample Soil (g) (g) (ppm) (ppm)(ppm) A1 134.13 55.6800 NA 0.015 0.019 A2 134.28 56.1870 NA 0.028 0.034A3 134.27 63.5577 NA NA 0.016 A4 134.22 59.1784 NA 0.017 0.026 A5 134.2863.5230 NA NA 0.013 B1 134.30 59.4055 NA NA 0.017 B2 134.25 59.2633 NA0.015 NA B3 135.55 57.1100 NA 0.017 0.023 B4 134.43 60.2596 NA NA 0.016B5 134.11 53.8605 NA NA 0.015

TABLE 4 Solution Collected Au Ag Hg Sample Soil (g) (g) (ppm) (ppm)(ppm) A1 134.13 55.6800 NA 0.112 0.141 A2 134.28 56.1870 NA 0.209 0.251A3 134.27 63.5577 NA NA 0.118 A4 134.22 59.1784 NA 0.128 0.194 A5 134.2863.5230 NA NA 0.095 B1 134.30 59.4055 NA NA 0.124 B2 134.25 59.2633 NA0.115 NA B3 135.55 57.1100 NA 0.122 0.169 B4 134.43 60.2596 NA NA 0.121B5 134.11 53.8605 NA NA 0.108

From these data it is apparent that all of the solutions that containeda clay stabilizer (A2-A5) had more leach solution collected through thecolumn than the blank solution with no clay stabilizer. CS-1420 andEthox 4439 filter much more quickly through soil than the solution withno treatment (A1), and solutions prepared with CS-1550 and CS-1420ST.Metal determination data suggested that the concentration of metal inthe soil was too low to obtain results that were much greater than thedetection limits of the methods.

EXAMPLE 2

A column which was 0.914 M (3 feet) tall and 5.08 cm (2 inches) indiameter was fitted on one end with a plastic Buchner funnel. The columnwas charged with 1300 grams of soil filling about ⅔ of the column. Thecolumn was tapped hard onto a rubber pad about 20 times to ensure thatthe soil was tightly packed. Two liters of solution were preparedcontaining 500 ppm NaCN and 0.1% NaOH in deionized water and additive asindicated in Table 5. The solutions were poured into the top of thecolumn, above the soil to wet the soil, and the excess amountcontinuously fed from this beaker into the top of the column by a pump.Any overflow was returned to the source beaker by way of an overflowtube thereby maintaining approximately 12 inches of solution on top ofthe soil. The column effluent was captured in a separate beaker on a toploading balance with 0.1 gram of readability. The mass was recordedautomatically into a data file. An increase in the time required for theflow to cease, as measured by the weight of effluent remainingsubstantially unchanged, was defined as an indication of a decrease inthe blockage of flow passages with a rate of 0.05 g/min used as theendpoint. Many samples were tested with a subset of the results providedin Table 5 and illustrated graphically in FIG. 1.

From the graph it is apparent that the rate of collection of controlsolution, which contained no additive, slowed considerable after 25hours, when approximately 800 grams of solution had been collected.Solutions which contained additives maintained a higher flow rate for alonger period of time. The additive ERS 02257 is a commerciallyavailable ethylene oxide-propylene oxide-ethylene oxide copolymeravailable from Ethox Chemicals LLC as ETHOX 4439 or P-104. ERS 02258 isa terpolymer of dicyandiamide and formaldehyde and ammonium chloride.Measurement of the sample containing 0.1% ERS 02257 was aborted due totechnical difficulties.

A particularly preferred embodiment is a mixture of clay stabilizingpolymers, indicated as “ERS 02257 and 02258 blend” in the graph. Thissolution continued to flow through the soil beyond 60 hours, at whichtime over 1400 grams of solution were collected. The major component ofthe blend, ERS 02254 (Ethox P-104) which is a block copolymer ofapproximately 54 moles of propylene oxide and 64 moles of ethylene oxideon diethylene glycol. The material has a molecular weight ofapproximately 6000 Daltons. The second material, ERS 02258 (CS-1550) isa material that is sold by Polymer Ventures, Charleston, S.C., and ispromoted by that company to be a clay stabilizing agent.

As described in Table 5, the 0.2% blend of ERS 02257 and ERS 02258showed the greatest improvement in terms of time (233%) and amount ofsolution filtered (184%). Of the 0.2% blend, 75% consisted of ERS 02257,25% was ERS 02258. Field testing of this material at a gold mineconfirmed greater throughput of material as compared with solution thatdid not contain this blend.

EXAMPLE 3

Laboratory testing continued during field trials of the 0.2% blend ofERS 02257 and ERS 02258. The test method was modified from thatdescribed in Example 2, to decrease total test time so more materialscould be evaluated in a shorter amount of time. The same test column wasused (3 feet long, 2 inch diameter), the same amount of ore (1300 grams)was packed into the column. In these tests all solutions were made with0.2% additive and the same concentrations of sodium cyanide and sodiumhydroxide as used previously. One liter of solution was tested, ratherthan 2 liters of solution, and the solution was passed through the oreonly a single time, rather than recirculated. As before, the mass wasmonitored as a function of time. Mass of pregnant solution collected wasplotted as a function of time in the graphs shown in FIGS. 2 and 3. Inthese graphs, plots obtained for treated solutions may be compared toplots obtained from data collected for a control solution (labled“blank” in FIGS. 2 and 3). This aqueous solution contained only sodiumcyanide and sodium hydroxide. The objective of this test is to identifyadditives that prevent pooling of solution when it is placed on a heapof ore. Solutions that prevent pooling are expected to pass through theheap at a faster rate.

Voranol CP 6001 Polyol, a glycerol, propylene oxide, and ethylene oxidepolymer, which is sold by Dow Chemicals, was evaluated as a replacementfor ERS 02257.

Wetting agents were evaluated for replacement of ERS 02258 in the blend.Compounds which are commonly used as soil wetting agents were chosen forevaluation. A blend of 75% Voranol CP 6001 and 25% dioctyl sodiumsulfosuccinate (DOSS) performed well in the filtration test, shown inFIG. 2, plotted with long dashes, as compared with the original blend(75% ERS 02257 and 25% ERS 02258), shown in the gray trace with the longdash and dot, in the same figure. A faster flow rate was observed forthe solution which contained 75% Voranol CP 6001/25% DOSS.

The Voranol CP 6001/DOSS blend was found to separate upon aging.Adjustment of the blend to pH 5 with hydrochloric acid preventedseparation. The pH was readjusted to pH 10 with ammonium hydroxide andthe material remained in a single liquid phase. This reformulated blendwas clear and was found to perform well in ore extraction laboratorytests (compare the solid dark grey trace in FIG. 3 labeled.

Voranol 6001/DOSS/HCl/NH₄OH to the dashed gray line labeledCP/6001/DOSS). A second material from Dow, 222-029 polyol, apolyalkylene glycol, was also evaluated as a replacement for ERS 02257.A blend of 75% 222-09 and 25% DOSS solution performed as well as theVoranol CP 6001/DOSS solution.

Other blends were prepared using Voranol CP 6001, their plots are shownin FIGS. 2 and 3. All but one of these showed improvement in flow ofsolution through ores, as compared with the untreated solution, labeled“blank”. The other wetting agents tested were: hexylene glycol; acombination of DOSS and ERS 02258; decyl alcohol with 2 moles propyleneoxide (PO) and 4 moles ethylene oxide (EO), labeled 1437; undecylalcohol with 7 moles of EO, labeled 4374; a blend containing tridecylalcohol with 9 moles of EO labeled 4708; decyl alcohol with 4 moles ofEO labeled DA-4; decyl alcohol with 6 moles of EO, labeled DA-6; diamylphenol with 10 moles of EO, labeled DAP-10; octyl-decyl alcohol with 4moles each of PO and EO, labeled 2848. The results shown in FIGS. 2 and3 may be compared in terms of two attributes, wetting and flow rate.Wetting speed is indicated by the amount of time it took to begincollection of solvent. The wetting time of the control (labeled “blank”and indicated by solid black line) was tested twice and was found to be1.5 and 2 hours, as indicated by FIGS. 2 and 3 respectively. Nearly allof the solutions which contained additives has shorter wetting speedsthan the control solution.

Flow rates may be compared by reporting the amount of time required topass 550 grams of each solution through the column. This mass representsa time when a significant portion of the solution has passed through thecolumn, wetting the ore, and yet some of the liquid solution remains ontop of the ore and the ore has not become dry. These times are reportedin Table 6 for solutions that were tested in this example. All solutionswhich contained additives, except for the one prepared with VoranolCP6001 and Ethox 2848, had faster flow rates than the control sample(reported as “Blank”, based on the shorter elution time required tocollect 550 grams of solution.

TABLE 5 Stop time Improve- Stop mass Improve- Solution (hrs) ment(grams) ment Control (no additive) 30 NA 823 NA 0.1% ERS 02257 57 190%1172 142% 0.1% ERS 02257 and 60 200% 1289 157% 02258 (blend) 0.2% ERS02257 and 70 233% 1514 184% 02258 (blend)

TABLE 6 Time required to collect 550 grams of solution containing theindicated additive. Additive Hrs:min CP6001/1437 4:27 Voranol CP6001/DOSS* (3:1) 4:54 Voranol CP 6001/DOSS‡/HCl/NH₄OH 5:07 CP6001/43745:20 Voranol CP 6001/Hexylene glycol (3:1) 5:28 Voranol CP 6001/DOSS‡(9:1) 6:20 222-029 Polyol/DOSS* (3:1) 6:40 ERS 02257 and 02258 (3:1)8:03 CP6001/4708 8:52 8000/Hexylene glycol/DA-4 (45:5:50) 9:15CP6001/DOSS‡/DA-4/HCl/NH₄OH 9:51 CP6001/DAP-10 10:58  CP6001/DOSS‡11:13  CP6001/DA-6 11:28  Voranol CP 6001/DOSS*/ERS 02258 12:21  DOSS‡12:23  Blank 12:58  Blank 13:26  CP6001/2848 14:57  *DOSS = Cytec OT-75†DOSS = Polywet 750 PG ‡DOSS = Ethox 4540

The invention has been described with reference to the preferredembodiments without limit thereto. One of skill in the art would realizeadditional embodiments and improvements which are not specifically setforth herein but which are within the scope of the invention as morespecifically set forth in the claims appended hereto.

The invention claimed is:
 1. A solution for leaching a metal from claycontaining ore comprising: cyanide; a wetting agent; and a claystabilizing polymer wherein said clay stabilizing polymer is selectedfrom the group consisting of polyalkylene oxide copolymer; propoxylatedglycols; polyamine copolymers comprising dicyandiamide, formaldehyde andammonia; polyvinyl alcohol; partially hydrolyzed polyvinyl acetate;polyacrylamide; quaternary amines; carboxymethyl cellulose; methacrylatecopolymers; hydroxyaldehydes; hydroxyketones; and copolymers of cationicmonomers.
 2. A solution for leaching a metal from clay containing ore ofclaim 1 wherein said metal is selected from the group consisting ofgold, silver, copper and uranium.
 3. A solution for leaching a metalfrom clay containing ore of claim 1 having a pH of at least 8 to no morethan
 11. 4. A solution for leaching a metal from clay containing ore ofclaim 3 having a pH of at least 9.5 to no more than 10.5.
 5. A solutionfor leaching a metal from clay containing ore of claim 1 comprising atleast 50 ppm cyanide to no more than 1000 ppm cyanide.
 6. A solution forleaching a metal from clay containing ore of claim 5 comprising at least200 ppm cyanide to no more than 800 ppm cyanide.
 7. A solution forleaching a metal from clay containing ore of claim 1 wherein said claystabilizing polymer is a tetramethylammonium salt.
 8. A solution forleaching a metal from clay containing ore comprising: cyanide; a wettingagent; and a clay stabilizing polymer wherein said clay stabilizingpolymer is selected from the group consisting of a polyalkylene oxidecopolymer, a propoxylated glycol and a polyamine copolymer.
 9. Asolution for leaching a metal from clay containing ore of claim 8wherein said polyalkylene oxide copolymer is defined by:R¹—R²—R³—R⁴—R⁵ wherein: R¹ and R⁵ are terminal groups independentlyselected from the group consisting of H, hydroxyl, saturated orunsaturated aliphatic of 1 to 30 carbons, and —OC(O)R⁶ wherein R⁶ is ahydrogen or a saturated or unsaturated aliphatic of 1 to 30 carbons; atleast one of R², R³ or R⁴ is polypropylene oxide (PO) having 1 to 100 POgroups; R², R³ or R⁴ is otherwise independently selected from the groupconsisting of polyethylene oxide (EO) having 1 to 100 EO groups,polypropylene oxide (PO) having 1 to 100 PO groups with the proviso thatat least one of R², R³ and R⁴ is not PO, polyester defined by—(OC(O)R⁷C(O)O)_(z)—wherein R⁷ is aromatic having at least one to nomore than four aromatic rings or a saturated or unsaturated aliphatichaving 1 to 20 carbons and z is an integer of 1 to
 100. 10. A solutionfor leaching a metal from clay containing ore of claim 9 wherein saidR², R³ or R⁴ is ethylene oxide having 2 to 100 EO groups.
 11. A solutionfor leaching a metal from clay containing ore of claim 9 wherein saidR², R³ or R⁴ is propylene oxide having 2 to 100 PO groups.
 12. Asolution for leaching a metal from clay containing ore of claim 9wherein z is an integer of 2 to
 100. 13. A solution for leaching a metalfrom clay containing ore of claim 9 wherein R³ is PO and R², R³ and R⁴are independently selected from EO and polyester.
 14. A solution forleaching a metal from clay containing ore of claim 8 wherein saidpropoxylated glycol is defined by the formula:X[(CH₂CHR¹⁷O)_(s)R¹⁸]_(t) wherein X is a linking group derived from anorganic compound containing at least two hydroxyl or amine groupscapable of reacting with ethylene oxide; R¹⁷ is independently —H or—CH₃, branched or linear aryl or alkyl moieties of 2-22 carbons or—CH₂OR¹⁹ groups such as those arising from the reaction of an alkyl oraryl glycidyl ether with the proviso that at least one R¹⁷ is nothydrogen; R¹⁸ is independently —H, aryl or alkyl hydrocarbon chains of1-25 carbons or —C(═O)R²⁰; R¹⁹ is a branched or linear aryl or alkylmoiety of 1-22 carbons; R²⁰ is aryl or alkyl hydrocarbon chain of 1-25carbons which may be saturated or unsaturated; s is an integer of 3-300;t is an integer of 2-12.
 15. A solution for leaching a metal from claycontaining ore of claim 8 wherein said propoxylated glycol is defined bythe formula:R¹⁰—CH₂—CH(OR¹²)CH₂(OCH₂CH(OR¹³)CH₂)_(n)OR¹¹ wherein R¹⁰ and R¹¹ areterminal groups independently selected from the group consisting of H,hydroxyl and saturated or unsaturated aliphatic of 1 to 30 carbons or—OC(O)R¹⁵ wherein R¹⁵ is a hydrogen or a saturated or unsaturatedaliphatic of 1 to 30 carbons; R¹², R¹³ are independently selected frompolyethylene oxide (EO) having 1 to 100 EO groups; polypropylene oxide(PO) having 1 to 100 PO groups or —(CH₂CHR¹⁶O)_(r)—; R¹⁶ isindependently hydrogen or methyl; r is an integer of 1 to 100; and n isan integer of 1 to
 4. 16. A solution for leaching a metal from claycontaining ore of claim 15 wherein r is an integer of 2 to
 100. 17. Asolution for leaching a metal from clay containing ore of claim 15wherein said R¹², R¹³ are independently ethylene oxide having 2 to 100EO groups.
 18. A solution for leaching a metal from clay containing oreof claim 15 wherein said R¹², R¹³ are independently propylene oxidehaving 2 to 100 PO groups.
 19. A solution for leaching a metal from claycontaining ore of claim 8 wherein said polyamine comprisesdicyandiamide, formaldehyde, and ammonia.
 20. A solution for leaching ametal from clay containing ore of claim 19 wherein said polyamine has ahydroxyl number of at least 20 to no more than
 35. 21. A solution forleaching a metal from clay containing ore of claim 20 wherein saidpolyamine has a hydroxyl number of at least 26 to no more than
 31. 22. Asolution for leaching a metal from clay containing ore comprising:cyanide; a wetting agent wherein said wetting agent is selected from thegroup consisting of alcohol ethoxylates; polyethylene glycol esters,hydrophilic modified silicones, and fatty amine ethoxylates; and a claystabilizing polymer.
 23. A solution for leaching a metal from claycontaining ore of claim 22 wherein said alcohol ethoxylate has an alkylchain having 5-20 carbon atoms.
 24. A solution for leaching a metal fromclay containing ore of claim 23 wherein said alcohol ethoxylate has analkyl chain having 10-15 carbon atoms.
 25. A solution for leaching ametal from clay containing ore of claim 22 wherein said alcoholethoxylate has 2 to 20 ethylene oxide units.
 26. A solution for leachinga metal from clay containing ore of claim 25 wherein said alcoholethoxylate has 3 to 14 ethylene oxide units.